Further studies on biochemical characteristics and serologic properties of the genus Aeromonas.

We characterized a collection of 268 Aeromonas isolates from diverse sources (clinical, animal, and environmental sources) for their species and serogroup designations. Overall, 97% of these strains could be identified to the genomospecies level by using an expanded battery of biochemical tests. Members of the Aeromonas hydrophila complex (A. hydrophila, HG2, and A. salmonicida), a group that has previously been difficult to separate biochemically, could easily be distinguished from one another by using a number of recently described phenotypic properties which included utilization of DL-lactate and urocanic acid. Differences in species distributions on the basis of the source of isolation were noted. Serogroup analysis of these 268 isolates plus a number of reference cultures indicated that (i) each genomospecies is serologically heterogeneous and individual serogroups can be found in more than one species, (ii) most type or reference strains for each hybridization group are not serologically representative of the genomospecies at large, (iii) serogroups O:11, O:34, and O:16 predominate clinically (48%), supporting previous studies indicating their importance in human infections, and (iv) most A. trota strains do not express the O139 antigen of Vibrio cholerae. The collective results suggest that both species and serogroup designations are important factors in establishing which isolates can cause human infections when they are acquired from nonclinical sources (foods, animals, and the environment).